Barred Sand Bass Essential Fishery Information

Essential Fishery Information (EFI) includes data on age, growth, reproduction, and other life history characteristics that are important for managing a sustainable fishery. During the 1980s, barred sand bass (Paralabrax nebulifer) became increasingly popular; up to an estimated 4.2 million barred sand bass were caught by recreational anglers in 1988. Catches remained high into the 1990s; however, fishery-dependent and fishery-independent data sources suggest significant population declines over the last decade.

Fish populations may adapt to exploitation over time by increasing recruitment and/or growth rates, or by reducing natural mortality. However, at high levels of exploitation, a population may reach a critical low, becoming less resilient and moving toward depletion.

Regulatory changes adopted in 2012 set the minimum size limit for the saltwater basses at 14 inches, and the bag limit to 5 fish in any combination of barred sand bass, kelp bass and spotted bass. These regulations went into effect on March 1, 2013 (see new size and bag limits It will likely take several years before the effectiveness of recent management changes can be assessed; however, data collected in this project will provide managers with the knowledge necessary to detect fishery concerns earlier and prevent overfishing.

Data on several reproductive, age, and growth parameters for barred sand bass are outdated or lack adequate sample sizes, and no data exist on barred sand bass spawning periodicity (fluctuations in reproductive hormone levels). These EFI are needed to evaluate the fishery's response to recent and future regulation changes, as well as oceanographic changes. In addition, these EFI will be critical components of future stock assessments and fishery management plans, further enhancing the CDFW's ability to manage this species.

The project collected EFI for barred sand bass on spawning frequency, spawning periodicity and batch fecundity and the results of these data were published in Jarvis et al. 2014 (PDF). Data on age structure and validation are still being analyzed.

Barred sand bass, Paralabrax nebulifer, are one of the most sought-after sport fishes in southern California. Since the 1960s, this species has ranked among the top ten sport fish caught by commercial passenger fishing vessels (CPFVs), or "party boats," in southern California, with annual catches averaging nearly one million fish over the last 20 years. For decades, CPFVs and private recreational boaters have targeted well-known spawning aggregation sites throughout southern California, including the Ventura Flats, Santa Monica Bay, Huntington Beach Flats, San Onofre, and San Diego. Approximately 71 percent of the annual barred sand bass catch is harvested by the CPFV fleet from June through August, during peak spawning season.

Records show that from 1961 to 2000 barred sand bass catches increased, followed by a dramatic decline in landings through 2008. These dramatic catch declines in recent years have caused concern among fisheries biologists and fishermen alike. A 2010-2011 fishery analysis on the basses (including barred sand bass) indicates that bass populations in the last decade have been negatively affected by cool oceanographic conditions and fishing. Answering scientific questions regarding barred sand bass spawning behavior, movements and spawning habitat requirements will be important for the management of this resource.

Barred sand bass catch location data was compiled by California Recreational Fisheries Survey samplers for private/rental boats from 2004-2008 in the southern California region. Samplers interview anglers at public launch facilities, ask questions about their fishing activities, examine their catch to determine the number and species of fish kept or discarded, weigh and measure the catch, and collect fishing location and depth information. The catch location data were mapped and analyzed and major "hotspot" catch locations (potential spawning grounds) were identified using a Geographic Information System. This analysis provides valuable information about where and when barred sand bass spawning aggregations may occur in southern California. In addition, areas fished around Huntington Beach were examined on a finer scale to examine any seasonal patterns of catch.

Spawning Movements

In the 1960s and 1990s, CDFW biologists tagged a total of 9,000 barred sand bass in southern California. The recapture information from these two time periods enabled us to document large-scale spawning-related movements of barred sand bass for the first time. Using this dataset we attempted to discover:

How long individual barred sand bass remain at spawning grounds during spawning season

How far fish migrate to spawn

Whether fish show fidelity to certain spawning locations

In addition to large-scale spawning movements, we were also interested in the short-term, fine-scale spawning movements of barred sand bass. To address this, project staff worked with California State University, Long Beach professor Dr. Chris Lowe and his master's student, Megan McKinzie. Project staff assisted with field research that uses state-of-the-art technology to actively track adult barred sand bass at Huntington Flats during the spawning season. Fish were surgically fitted with acoustic transmitters and then followed by boat using an underwater hydrophone. Several transmitters contained depth sensors which emitted a signal that allowed the researcher to determine both the horizontal and vertical movements of the fish every two seconds.

The results from this research allowed us to characterize fine-scale horizontal and vertical movement patterns of tagged barred sand bass during the spawning and non-spawning seasons, and to quantify activity space size (area and volume), habitat use and preference, and patterns of activity throughout a 24-hour period. Movement patterns believed to be indicative of spawning and/or courtship were determined through the comparison of spawning and non-spawning season individuals.

(1) With the fish immersed in a saltwater anesthetic bath, the transmitter is inserted through a small incision in the lower abdominal cavity.
(2) Two to three sutures are used to close the incision.
(3) Prior to release, the fish is measured and fitted with an external dart tag for easy identification upon recapture.

CDFW photos by E. Jarvis

Spawning Habitat

The timing and location of spawning aggregations are related to water temperature, lunar activity, and currents for some other aggregate spawners. However, depth and bottom habitat type are the only characteristics documented in historical descriptions for barred sand bass spawning aggregation sites. To understand whether barred sand bass spawning aggregation sites were unique, Fisheries Independent Assessment Project staff conducted field surveys in 2008 to determine the typical oceanographic (water temperature), seafloor habitat (type of substrate), and biological features (invertebrates living on and in the substrate) of areas where barred sand bass spawning aggregations occur and areas where they are absent.

During the summer months, five "hotspots" for barred sand bass catch were identified that are likely major spawning grounds for this species. The proportion of catch varied among these "hotspots" from 2004 to 2008 with Huntington Flats off Orange County and Imperial Beach ("I.B." Flats) on the U.S./Mexico border in San Diego County being the top catch locations. On a finer scale, natural reefs (Horseshoe Kelp and Palos Verdes Peninsula) and artificial structures (reefs, oil rigs, and breakwaters) were more important catch locations in the Huntington Beach Flats area outside of peak spawning season. This suggests that areas with higher relief or structure may serve as important habitat for barred sand bass before and after spawning activities.

Map of the Southern California Bight showing the number of barred sand bass kept and released by private/rental boats from 2004-2008 by 1x1 mile fishing block from June - August. The percentages represent the proportion of barred sand bass caught by county and standardized by area (1x1 mile fishing block).

Spawning Movements

Tag and Recapture Data

The CDFW received 972 barred sand bass tag returns from tagging efforts conducted in the 1960s and 1990s (an 11 percent recapture rate). Based on recapture frequencies, it appears that barred sand bass individuals remain on spawning grounds (e.g., Huntington Beach Flats) for at least one month during peak spawning season. Spawning residency at Huntington Flats was estimated by the frequency of returns over time; most same-year returns (82%, n = 141) were recaptured within a 35-day period, with secondary peaks in returns at 28 and 56 days at liberty.

Frequency of tag returns over time for fish tagged during peak spawning season (June through August)
at Huntington Flats and recaptured there within the same year.

Following spawning season, some fish remain, while others move away. The average migration distance from spawning locations was about 15 miles, although it appears that not all individuals at spawning grounds migrate to the same locations after spawning season. Overall, the farthest recapture distance was approximately 57 miles. Annual patterns in the timing and occurrence of recaptures strongly suggest barred sand bass visit the same spawning grounds year after year.

Three distinct patterns of behavior were identified and believed to be representative of non-spawning season behavior, spawning season resting behavior, and spawning/courtship related behavior. Non-spawning season fish remained more closely associated with reef habitats than sand habitat, used smaller activity spaces, and remained more closely associated with the substratum than fish tracked during the spawning season.

Fish tracked during the spawning season used significantly more area and volume, and preferred sand over available reef habitats than fish tracked during non-spawning season. Spawning season fish typically utilized more of the available water column; individuals made dives toward the seafloor throughout the day and remained close to the seafloor at night. During the day, they remained primarily within or just below the thermocline (~ 16 °C), but continually made directed dives towards the seafloor lasting 15 to 30 seconds, a behavior believed to be analogous to vertical spawning rushes demonstrated by other serranids. Fish tracked during spawning season also demonstrated movement patterns similar to non-spawning season fish and was believed to be resting behavior.

Box and whisker plots of day versus night activity space-area during spawning and non-spawning seasons.

Box and whisker plots showing distance from bottom during day and night periods for both spawning and non-spawning fish.

Not surprisingly, our results indicated the Huntington Flats largely consists of a uniform, sandy substrate; however, our analysis of existing substrate maps also identified several previously unknown areas of hard substrate sparsely scattered over the study area. Exploratory scuba dives conducted by CDFW staff identified barred sand bass on these reefs (some natural, some artificial) during peak spawning season, but we never observed courtship or spawning behavior even though dives occurred during daylight hours when barred sand bass reportedly spawn. Although there is potential barred sand bass spawning over reefs, the reefs may actually serve as areas for reproductive staging, resting, refuge, and foraging during spawning season.

The distribution of observed CPFV activity on barred sand bass spawning aggregations did not appear related to the distribution and (or) relative abundances of larger bottom invertebrates and animals that dwell within bottom sediments/sand. Fishermen have long associated barred sand bass spawning aggregations with "clam beds"; however seafloor video footage taken during opportunistic events on the Flats did not reveal evidence of large clam beds in the area. Although we did not collect sand bass stomachs for stomach content analysis, as they become adults barred sand have been shown to shift their diet predominantly to fishes that live near the bottom and crabs. Therefore, although clams occurred frequently in our benthic survey of the Flats, barred sand bass probably form aggregations over sand flats for reasons other than the presence of clams or other soft bottom prey items.

Hard and soft substrate mapped within the Huntington Flats study area in southern California in 2008.
Data source: California Seafloor Mapping Project.
Some areas beyond state waters (3 nm) were not available.
Circled numbers reference small patches of hard substrate within the study area. AR=artificial reef.

Oceanographic Conditions at Huntington Flats

The development of a strong thermocline occurred during late July and early August and coincided with the highest, sustained catch of barred sand bass during peak spawning season. Thermocline temperatures measured within areas of presumed aggregation activity were significantly warmer than the average thermocline temperatures measured throughout the area during June, July, and August. In subsequent years, barred sand bass tracked during spawning season were associated with the thermocline during the daytime (see Fine-scale Movements above). Previous research on the optimal thermal habitat for barred sand bass egg and larval development suggests warmer thermocline temperatures may increase larval fitness.

Comparison of average thermocline temperatures on the Huntington Flats in June, July, and August, and during sampling events located within barred sand bass aggregation fishing activity, 2008. Error bars represent 95% confidence intervals, the asterisk denotes a statistical difference among means.

Daily catches of barred sand bass by the CPFV fleet were positively associated with fishing effort and tidal flux, and negatively associated with chlorophyll-a concentrations. These factors explained 72 percent of the variability in barred sand bass catch over the peak spawning season. Periods of high tidal flux occurred during both new and full moon phases; thus, the observed peaks in barred sand bass catch may represent a reproductive behavioral response to tidal amplitudes more so than moon phase. Sea surface currents were generally low during peak barred sand bass catches; however, Huntington Flats experienced large tidal fluxes of several feet.

The negative relationship between barred sand bass CPFV catches and chlorophyll-a concentrations is less clear. Chlorophyll-a concentrations are typically used as a proxy for phytoplankton abundance and tend to be inversely related to the ability of light to penetrate water in this area. A negative relationship with chlorophyll-a may reflect a preference of barred sand bass aggregations for increased water clarity, or it may reflect avoidance of forage fishes that eat plankton and zooplankton egg predators.

Understanding the reproductive potential of barred sand bass depends not only on how long fish stay at a spawning aggregation but how frequently they spawn. We can tell if a female has recently spawned by the presence of postovulatory follicles in the ovaries. When we know what proportion of females have postovulatory follicles, we can estimate spawning frequency. In a previous study, female barred sand bass were shown to spawn about every day and a half, but most samples were collected toward the tail end of peak spawning season and so frequency intervals may have been underestimated. To re-examine spawning frequency, 248 barred sand bass were collected from the Huntington Flats spawning grounds over the course of the spawning season (June through August 2011), gonads were removed and histologically sectioned and stained to visualize the internal gonadal structures and to identify postovulatory follicles.

Histological section from ovary of a barred sand bass collected at the Huntington Flats spawning aggregation.
Several stages of oocyte development are present. Postovulatory follicle is labeled.

Findings to Date

The previous spawning fraction and spawning interval estimates for barred sand bass were taken over a two week period in July. To determine if these estimates vary across the spawning season, we quantified ovarian activity using histological cross-sections from 208 barred sand bass females collected on the San Pedro Shelf from June to September 2011. We were able to classify the overall reproductive state of the ovaries and assign them reproductive phases. We found the typical monthly reproductive phases to be:

June (developing: ovaries beginning to develop but not ready to spawn)

July and August (spawning capable: fish are developmentally capable or actively spawning)

September (regressing: cessation of spawning)

The spawning fraction (S) was estimated using the postovulatory follicle (POF) method to determine the proportion of mature females with POFs < 24 hours old. The spawning fraction varied by month (x2 (3, N =208) =23.1, p < 0.001) with the proportion of spawning females peaking in July and August, although no difference was noted between these two months (x2 (1, N =166) =0.836, p = 0.361).

During July and August spawning season (S =0.54, upper 95% confidence limit=0.6220 and lower 95% confidence limit=0.4722), the average spawning interval was 1.85 days, with daily spawning in 42% of fish. In contrast, POFs were less abundant in June (S = 0.17, upper 95% confidence limit=0.3467 and lower 95% confidence limit=0.0607) and September (S =0.11, upper 95% confidence limit=0.3405 and lower 95% confidence limit=0.0186), further indicating spawning season lasts from July-August.

We compared the monthly proportion of recently spawned fish, (fish that spawned within four hours of capture), and found July was significantly higher than August (x2 (1, N =166) =6.75, p = 0.009) indicating spawning peaks in July. Our results highlight the importance of sampling throughout the spawning season in order to avoid over- or underestimating the total number of spawning events per individual per year.

Spawning is triggered in many species by environmental cues. In marine environments, common cues include lunar and/or tidal flux. These cues are important for species to mate successfully and may indicate the best times for survival of fertilized eggs and larvae. Barred sand bass may experience other environmental cues such as increased day length or increased temperature that drive them to form spawning aggregations, but there may also be additional, closely related environmental cues throughout the spawning season that trigger spawning pulses. Understanding which cues trigger spawning in barred sand bass is important for understanding how and why reproductive potential sometimes varies from year to year.

Reproductive hormones fluctuate with respect to environmental cues and may peak during spawning pulses. By analyzing hormone concentrations in barred sand bass over the course of the breeding season, we may determine if there is a relationship with lunar cycles and/or tidal flux. To determine the relationship between environmental cues and spawning, blood plasma was collected from 264 barred sand bass over the course of the 2011 spawning season at the Huntington Flats spawning grounds to test for concentrations of estradiol, progesterone and 11-ketotestosterone (11-KT). Staff also seek to determine how hormone concentrations relate to fish size, gonad size and the presence/absence of post-ovulatory follicles produced by females following spawning events.

Findings To Date

We obtained blood plasma from 264 barred sand bass (160 females, 102 males, 2 unknowns) to analyze reproductive hormone levels (estradiol, 11-KT, progesterone) during spawning season. We calculated mean hourly and weekly levels of each hormone to identify any peak(s) in hormone concentration during a 24-hour period and during spawning season. We were able to collect blood plasma samples between the hours of 7:00 a.m. and 3:00 p.m. During those times, female levels of estradiol in July and August were significantly higher before noon than after noon.

Estradiol (July and August)

Estradiol levels in female barred sand bass collected in July and August of 2011 were significantly higher before noon than after noon (collection hours were 7:00 a.m. to 3:00 p.m.).

Male levels of 11-KT peaked once during the week of July 20. 11-KT triggers spermatogenesis in males and so the peak in late July suggests most males have reached their peak in potential reproductive output (i.e., high GSI due to proliferation of spermatozoa) by the end of July. Relatively low levels in late June and August were similar to values obtained on a single sampling date in mid-September.

11-ketotestosterone

11-ketotestosterone levels in male barred sand bass peaked once during the 2011 spawning season, in late July.

Female levels of estradiol peaked in late June, late July, and mid-August. The peaks in July and August were of similar magnitude, and by late August/early September estradiol levels had fallen again. By mid-September, estradiol levels in 9 females were near zero, indicating spawning had already ceased. Preliminary analyses suggest estradiol levels may be influenced by ocean temperature.

Estradiol

Estradiol levels in female barred sand bass peaked three times during the 2011 spawning season, with the highest peaks occurring in late July and mid-August.

Female levels of progesterone were relatively stable from late June until mid-August. Peaks in progesterone occur at the end of spawning season; the highest peak in female levels of progesterone occurred in late August.

Progesterone

Progesterone levels in female barred sand bass remained relatively stable through June and July before peaking in mid-to-late August.

Barred sand bass are serial spawners, meaning they may spawn many times over the course of a spawning season. As in other serial spawners, barred sand bass ovaries contain eggs at several different stages of development; however, only the hydrated eggs will be spawned. Batch fecundity refers to the number of eggs released in one spawning event. By determining the batch fecundity for several individuals over a wide size range, we can develop a batch fecundity-size relationship which will allow us to estimate the batch fecundity of females measured in the field. Batch fecundity will be an important parameter for estimating reproductive potential of barred sand bass. Staff collected gonads from 248 barred sand bass at the Huntington Flats spawning grounds over the course of the 2011 spawning season. Staff will count the number of hydrated eggs in the ovaries to determine batch fecundity for individual fish.

Findings to Date

Reliable batch fecundity estimates are essential for calculating total annual fecundity; however, previous batch fecundity studies on barred sand bass contained small sample sizes. We collected barred sand bass throughout the 2011 spawning season (June-August) and into September.

Batch fecundity was calculated using the hydrated oocyte method, where the number of hydrated oocytes was counted per 0.10 g of whole-mounted ovarian tissue and multiplied by ovary mass. Active or imminent spawning females were identified by the presence of hydrated oocytes and post-ovulatory follicles (POFs) in histological cross-sections taken from the ovaries of 208 females. Ovaries were categorized by POF age (Day 0= <4 hours, Day 1 = 4-24 hours, Day 2 = >24 hours), but only females with Day 2 POFs (n = 46) were used for obtaining a batch fecundity size relationship.

Based on the preliminary model predicted from females with Day 2 POFs (n =18), hydrated oocyte counts for a subset of females with Day 0 (n = 6) and/or Day 1 (n = 13) POFs underestimated batch fecundity by an average of 26% and 20%, respectively. Batch fecundity was linearly related to ovary mass (y = 1107x + 5147.5, R2 = 0.93) and the relationship with fish standard length (mm) was best described by the power function, y = 0.0086x2.8028, R2 = 0.72. None of the females collected in September met the criteria for estimating batch fecundity.

Cross-section of a sagittal otolith taken from a barred sand bass collected in the 1990s. The otolith was aged to 17 years. CDFW file photo.

The age of most finfish can be determined by analysis of their otoliths. Otoliths are hard structures located in the inner ear that grow as the fish grows by adding layers of calcium carbonate. The addition of layers is affected by seasonal changes in growth rate, so that calcium carbonate rings may form annually and can be counted similar to tree rings. We collected otoliths from 352 barred sand bass at Huntington Flats in 2011. By counting the rings on the otoliths we can estimate the age structure of barred sand bass at the Huntington Flats spawning aggregation in 2011. While this is a common ageing technique in fish, no one has ever validated that the ring pattern is annual across size classes in barred sand bass. To examine this, we will keep barred sand bass of several size classes in captivity for at least one year. Shortly upon capture we will inject a chemical marker called oxytetracyline (OTC) into the musculature that will be naturally incorporated into the otoliths. After a year, we will remove the otoliths and confirm the periodicity of the ring pattern.